Acetic acid is a weak acid in water because it is:
a. only slightly soluble.
b. completely dissociated into hydronium ions and acetate ions.
c. dilute.
d. unable to hold onto its hydrogen ion.
e. only slightly dissociated into ions.

The correct answer is e. only slightly dissociated into ions.

Explanation:

Acetic acid (CH₃COOH) is one of the best known weak acids. It dissociates into its ions as follows:

CH₃COOH (aq) ⇄ H⁺ (aq) + CH₃COO⁻ (aq)

The dissociation constant Ka is low: aproximately 1.75 x 10⁻⁵. That indicates the equilibrium is shifted to the left and the acid is only slightly dissociated into its ions (H⁺ and CH₃COO⁻).